The present invention relates to methods and apparatus for controlling starters of motor vehicles, and more precisely to methods and apparatus for driving the core of the contactor of the said starters.
As is shown in FIG. 1, a motor vehicle starter conventionally comprises a contactor 2 and an electric motor M, the output shaft of which carries a pinion 1. The pinion 1 is adapted to come into meshing cooperation with the starter crown C of the heat engine. It slides on the motor shaft M between a position in which it is disengaged from the said starter crown and a position in which it meshes with the latter.
The contactor 2 extends parallel to the electric motor M, above the latter, and includes a coil 2a and a plunger core 2b. 
It controls the power supply of the electric motor M by displacement of a moving contact 3 between an open position and a closed position, the said contact 3 being pushed by the said plunger crown 2b, which is movable axially with respect to the electric motor M when the coil 2a is energised.
The contactor 2 also controls displacement of the pinion 1. Its plunger core 2b is, for that purpose, connected to the pinion 1 by mechanical means indicated as a whole by the reference numeral 4.
These mechanical means include a fork which is attached at its upper end to the plunger core 2b and at its lower end to a starter head of which the pinion 1 is a part.
The starter head includes a free wheel which is interposed axially between a hub and the pinion 1. The hub has internal helical splines which engage with complementary external helical teeth carried locally by the output shaft of the electric motor M.
The fork is mounted for pivoting movement between its two ends on a casing which contains the mechanical means 4 inside it, and which carries the motor M and the contactor 2. The starter head with its pinion 1 is set in helical motion when it is displaced by the fork so as to engage with the starter crown.
This is achieved by energising the coil 2a following action by the ignition key which sets the plunger core 2b in motion, so that it is drawn towards a fixed core. mounted at the end of a support of the coil 2a. This support has a U-shaped cross section in order to contain the coil 2a, and accordingly has a base which constitutes a bearing 2c. The core 2b is therefore arranged to be displaced between a rest position and a contact position, in which it is in engagement on the fixed core, this closed position of the magnetic circuit being reached after the moving contact 3, and therefore the electrical circuit, are closed.
The mechanical means also include a return spring mounted around the core 2b so as to return the latter to its rest position, a cut-off spring associated with the moving contact 3 to return the latter to its open position, and a spring 5, called a clamping spring, which is mounted within the core 2b and is in engagement with a first rod coupled by a pivot pin to the upper end of the fork, for attaching the latter to the core 2b. This spring 5 has a higher stiffness than the return spring.
The fork is therefore interposed at its upper end between the core 2b and the pivot pin. The first rod, which is mounted within a blind hole in the core 2b, is arranged so that, after a predetermined course of travel, it comes into engagement with a second. rod fixed to the moving contact 3 and mounted for sliding movement within the fixed core. In the position where the contact 3 is closed, it cooperates with a fixed contact in the form of pads which are connected, respectively, to the positive terminal of the battery and to the electric motor M, thereby providing the power supply for the electric motor.
The pads are fixed to the closure cap of the contact, which is of insulating material.
All of these elements are shown in FIG. 1 and, in the interests of simplicity, have not been given reference numerals.
The pinion 1 is therefore able to come into engagement with the crown C, that is to say it can come into meshing engagement with the crown C before the moving contact has been closed.
Usually, the pinion 1 comes into axial abutting contact with teeth of the crown C before penetrating into the latter.
Thus, the mechanical means 4 include, in particular, a spring 5 which is interposed mechanically between the plunger core 2b and the pinion 1, and which enables the plunger core 2b to continue its course of travel whereby to ensure, before it makes contact with the fixed core, that the moving contact is put into its closed position even if the pinion 1 is prevented from moving by abutment against the teeth of the crown of the heat engine, in a position in which it is not meshing with the said crown.
Nevertheless, having regard to the rapidity of the movement of the moving core 2b and the elasticity of the mechanical coupling means 4, due in particular to the presence of the spring 5, substantial dephasing may occur between the closing of the contact 3 and the axial displacement of the pinion 1. Particularly at low temperatures, rotation of the electric motor, and therefore of the pinion 1, can be found to occur before the latter has had time to penetrate into the crown. Because the electric motor M is supplied at full voltage, the speed of the pinion 1 increases very fast, thereby preventing the pinion from meshing in the crown. The result is rapid destruction of crown and pinion.
In the document FR-A-2 679 717, it has been proposed to mitigate this disadvantage by supplying the contactor with a variable pulsed current.
With reference to FIG. 2, in this type of arrangement, a coil B controls both a contactor K and the forward displacement of a pinion, not shown. The coil B is supplied through a transistor T in pulse mode, of the pulse width modulation (PWM) type, the transistor being governed by a micro-controller 10. A cyclic ratio of the pulses is increased progressively so as to obtain an effective current in the coil which increases progressively. The purpose of this is to enable the moving core to begin its displacement with a minimum of magnetic attraction force and therefore with minimum acceleration, in order to avoid dephasing between the movement of the core and that of the pinion as described above.
This method also aims to reduce the velocity of impact of the pinion against the crown, whereby to reduce frontal wear in the latter.
However, it does not prevent violent displacement of the core from its rest position towards its working position.
In order to obtain a further reduction in this impact velocity, a method was proposed in the document U.S. Pat. No. 4,418,289, which conforms with the preamble to Claim 1, for supplying power to a coil for actuating a moving core of a contactor for an electric starter for a motor vehicle, wherein the effective current is varied in the coil during displacement of the core towards its contact position, and wherein, during this displacement, there take place:
a first driving phase at a high enough effective current to set the core in motion, and then,
a second driving phase with a weaker effective current.
The said document also proposes apparatus for control of the power supply to a coil for driving a moving contact of a motor vehicle starter, arranged to vary the effective current in the coil during displacement of the core towards its contact position, wherein it is arranged to perform, in the course of this displacement:
a first driving phase at an effective current sufficient to set the core in motion, then:
a second driving phase at a lower effective current.
In practice, it is arranged that, during the second phase, the electric motor is energised so that it rotates at reduced speed due to a supplementary disc having supplementary contacts and a supplementary resistor which are incorporated in the contactor. This second phase terminates on closing of the moving contact, which then cooperates with the fixed contact to energise the electric motor at full power.
This solution is not entirely satisfactory because it complicates the construction of the contactor.
In addition, it is not entirely reliable because, for example, the starter head and therefore the pinion can be prevented from moving.
An object of the present invention is to overcome these disadvantages in a simple and inexpensive way.
According to the invention, a method of the type mentioned above is characterised in that, during the second phase, when the moving core is not in its contact position, after a predetermined or determined time, a continuous increase in the effective current is initiated.
According to the invention, an apparatus of the type described above is characterised in that a continuous increase in the effective current is initiated during the said second phase after a predetermined or determined time.
Thanks to the invention, the contactor is of a simple form, and violent displacement of the core from its rest position to its working position is avoided.
In this connection, the effective current in the first time period of the second phase is less than the starting current in the solution in the document FR-A-2 679 717, because the core has already been released. Thus, noise is reduced and the solution is reliable.
In that connection, after a determined or predetermined time, the progressive increase of the effective current first enables the clamping spring 5 to be compressed, and secondly enables the contactor to close so as to energise the electric motor in the accidental case in which the contactor has been unable to be already closed.
Thus, in the accidental case where abnormally high friction forces occur in the contactor, in the mechanical means or in the region of the shaft of the electric motor, closing of the contactor is ensured after a predetermined or determined time.
Such cases can produce jamming as a result of particular climatic conditions, especially when the vehicle has been stationary for a long time. Dust and dirt can be lodged in the region of the fork and the shaft of the electric motor, and can therefore hinder displacement of the pinion.
The invention does nevertheless enable the starter head and its pinion to be displaced.
In addition, the pinion comes into abutting contact with the starter crown, either before the current is increased or after the current is increased and therefore the moving contact is closed, so that the electric motor is started from zero speed in this abutting contact position, which facilitates penetration of the pinion into the crown while reducing wear accordingly.
The solution according to the invention is therefore reliable and enables the useful life of the starter to be increased, in particular due to a reduction in wear.
Moreover, energy consumption and noise are reduced. The solution is inexpensive because the contactor can have only a single coil.
The invention makes it possible to carry out measurements during the first phase. This first phase can be divided into two time periods, namely a first time period in which the effective current is high, followed by a second period at a current lower than that in the second phase.
The second time period is preferably performed at zero current, so as to give the best measuring accuracy.
It is thus possible to measure the voltage in the battery during the first phase. During this first phase, the core is able to become unstuck after a shorter course of travel, the current during the first time period of this first phase being close to the current needed to cause the core to be so released, the phase being carried out with a shorter time period.
If some problems arise as a result, for example failure of the core to be released and failure of the contactor to close, these problems will be reduced in accordance with the invention because of the continuous increase in effective current intensity.
The limited release of the core enables shocks and violent displacements to be reduced even further, and also reduces energy consumption.
Thanks to the invention, the core has a double function, because, after a third time period in the second phase during which the intensity of the effective current is increased, it enables the moving contact to be held closed during a third phase after the electric motor has been started.
It will be appreciated that the electric motor only rotates after the pinion has come into engagement with the crown, so that the pinion is more easily able to penetrate into the crown, and so that wear is reduced.
The invention makes it possible to be at the limit of unsticking or release of the core in the first phase, so that the movement of the core is even more gentle.
The time is determined as a function of abnormal values which occur in the event of non-closure of the moving contact.
The time is determined for example as a function of the voltage in the battery or the temperature of the coil.
The time is easily determined in such a way that the continuous increase of current only takes place when required, that is to say the time can be made as short as possible, and this will embrace the majority of normal operating situations.